Device comprising an overlay mechanism, system with devices each comprising an overlay mechanism with an individually programmable delay or method for overlaying data

ABSTRACT

A device includes an overlay mechanism, system with devices each including an overlay mechanism with an individually programmable delay or method for overlaying data. A method for overlaying data includes redirecting an access which is directed to a first memory location to a second memory location. The method for overlaying data selectively delays access to the second memory location in case of a redirection by a time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application number 102016 218 280.3 filed on Sep. 22, 2016 in the name of Neil Stuart Hastie,entitled “DEVICE COMPRISING AN OVERLAY MECHANISM, SYSTEM WITH DEVICESEACH COMPRISING AN OVERLAY MECHANISM WITH AN INDIVIDUALLY PROGRAMMABLEDELAY OR METHOD FOR OVERLAYING DATA” and is hereby incorporated in itsentirety.

FIELD

Embodiments according to the disclosure are related to a devicecomprising an overlay mechanism. Further embodiments according to thedisclosure are related to a system comprising at least two devices.Further embodiments according to the disclosure are related to a methodfor overlaying data.

SUMMARY

An embodiment according to the disclosure creates a device comprising anoverlay mechanism configured or configurable to redirect an access whichis directed to a first memory location to a second memory location. Theoverlay mechanism is configured or configurable to delay access to thesecond memory location in the case of a redirection.

Another embodiment according to the disclosure creates a system,comprising a first device as described above, wherein the first devicecomprises a first processor. The system also comprises a second deviceaccording to one of the preceding claims, wherein the second devicecomprises a second processor. The system comprises a bus structurecomprising a plurality of bus segments and a plurality of memories. Thefirst processor and the second processor are coupled with the memoriesvia the bus structure. A delay of the overlay mechanism of the firstdevice and a delay of the overlay mechanism of the second device areprogrammable individually.

A method for overlaying data comprises redirecting an access which isdirected to a first memory location to a second memory location andselectively delaying access to the second memory location in case of aredirection by a time.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments according to the disclosure will subsequently be describedtaking reference to the enclosed Figures in which:

FIG. 1 illustrates schematically a device including the functionalprinciple according a first embodiment, wherein the device comprises anoverlay mechanism capable to perform a redirection of data and to delayan access to a second data location;

FIG. 2 illustrates schematically a second embodiment, wherein by meansof a data access a target memory and an overlay memory can be accessed,wherein a data access may be overlayed from the target memory to theoverlay memory;

FIG. 3 illustrates schematically a third embodiment, wherein it isillustrated how an overlay access may be postponed by delaying orstalling some cycles;

FIG. 4 illustrates schematically a fourth embodiment and focuses how theinteraction between a device and a first and a second memory locationmay interact via a bus;

FIG. 5 illustrates a fifth embodiment being an enhanced version of theembodiment illustrated in FIG. 4 having multiple actors of at least oneof a device, a first type memory location and a second type memorylocation;

FIG. 6 illustrates a sixth embodiment being an enhanced version of theembodiment illustrated in FIG. 4 or 5, to illustrate how multiple bussesor bus segments may interact by means of at least one bridge forming theinterface between at least two bus segments or busses to be connected;

FIGS. 7a and 7b illustrate a device and the interface of the device to abus according to a 7^(th) embodiment, wherein there is a delay unitwithin the device (FIG. 7a ) or at the interface between the bus and thedevice (FIG. 7b ); and

FIG. 8 shows a flow chart of an embodiment illustrating a method howoverlaying data works including a subsequent access on second memorylocation.

DETAILED DESCRIPTION

In FIG. 1 a first device 1 is illustrated having, for example, at leasttwo external interfaces 2, 3. The first interface 2 is capable for anaccess directed to a first memory location and the second interface 3 iscapable for an access directed to a second memory location. Theinterfaces to access the first and the second memory location 2, 3 mayemploy the same physical and/or logical structure which may be a bus.Within the device 1 there is an overlay mechanism 4 controlling oradministrating an overlaying of data from a first memory location 5 to asecond memory location 7. The overlay mechanism 4 may be used by aprocessor (MP) 1 a being part of the device 1, and may, for example, beimplemented using a sufficiently fast hardware circuit (or,alternatively, using a micro-programmed circuit or a processor). Therebythe change in a location of data is not visible or can be invisible toan application software. Thus, the application software can interactwith the processor 1 a during product development. The productdevelopment may, for example, comprise calibrating engine managementsystems. This can be technically implemented since the change inlocation of the data is performed by hardware within the device 1. Thedevice 1 or the processor 1 a may, for example, be controlled by adebug/calibration system or by an application software being part of thedebug/calibration system. Also the application software may be executedon the device 1 or, more specifically, on the processor 1 a.

The device 1 comprising the overlay mechanism 4 or the correspondingmethod for overlaying data may be controlled by the processor 1 a withinthe device 1 requesting access to the first memory location. Theoverlaying mechanism 4 may be part of the processor 1 a or may be adedicated hardware associated with the processor (for example, coupledwith the processor using a memory interface). The processor 1 a itselfmay attempt to access data being stored in the first memory location. Insignal or data processing, the processor 1 a may forward a request toretrieve data being stored in the first memory location or to store datain the first memory location. Since, after redirection of data by theoverlay mechanism 4, the data is retrieved from the first memorylocation or stored in the second memory location instead of the firstmemory location, the overlay mechanism 4 transforms a request of theprocessor to retrieve data from the first memory location into a requestto retrieve data from the second memory location, wherein the secondmemory location may be in a physically different memory entity or memoryrange or memory structure when compared to the first memory location.Alternatively, a request of the processor 1 a for data being stored inthe first memory location may be transformed, by the overlay mechanism,to a request for data being stored in the second memory location. Theoverlay mechanism 4 is configured to or configurable to delay access tothe second memory location in case of a redirection. In other words, inthe case of a data read, the data obtained from the second memorylocation may, for example, be provided to the processor 1 a with someintentionally inserted “extra” delay (which is longer than a physicallyunavoidable delay for retrieving data from the second memory locationand for transporting the data from the second memory location to theoverlay mechanism). In the case of a data write, a signaling to theprocessor that the data write is completed may, for example, be delayed(intentionally) by the overlay mechanism.

The delay of the overlay mechanism 4 of the device 1 may, for example,be programmable. Also the method may comprise programming a delay ortarget access time which may be applied at least to delay access to thesecond memory location. For instance a user or human user may be able toestimate a time for accessing the first memory location and the delayfor accessing the second memory location. Since in this case the user iscapable to estimate the access times, a user can calculate or estimatethe additional delay of the overlay mechanism 4 or of the method foroverlaying data, so that an access to the second memory location cannotbe completed by the device 1 before (or faster than) an access to thefirst memory location would be possible.

As illustrated in FIG. 2 the first memory location 5 may be within atarget memory 6 at which the device 1, especially a processor 1 a whichmay be part of the device 1, may intend to store data (or from which theprocessor may retrieve data). Instead of storing data in the firstmemory location 5, the overlay mechanism 4 or a corresponding method foroverlaying data stores data in a second memory location 7 being withinan overlay memory 8. The (one or more) external interfaces 2, 3 may alsoaccess the respective target memory 6 and the respective overlay memory8.

A memory location 5, 7 may be a bit, a byte or a number of bytes withinone memory 6, 8. Alternatively a location 5, 7 may be an entire memory6, 8. A location 5, 7 may be dividable in ranges being a part or apartition of a location. The first memory location 5 and the secondmemory location 7 may, under some circumstances, be part of the samememory 6, 8. In this case the target memory 6 and the overlay memory 8are the same memory 6, 8. However, the first memory location and thesecond memory location are typically part of physically separatememories (for example, memories using different memory technologiesand/or memories having different access times).

In the overlay mechanism 4 there may by a programmable table of targetaddress ranges and an associated set of redirected address ranges to besubstituted if a data access is performed to the target access range.Thereby the redirected address ranges are within the overlay memory 8and/or in the second memory location 7. The change in location may notbe visible to application software interacting with the device 1 but maybe performed by hardware 4 within the device 1, preferably at request ofthe processor 1 a within the device 1, under control of adebug/calibration system. The programmable table may be part of thehardware 4. The overlaying mechanism 4 is preferably implemented withinhardware.

Hence, such a device 1 allows the logical translation of addresseswithout modification of application software. Hence, the device 1allows, for example, the Flash data tables to be overlayed by the SRAM.The application software may rely on the device 1 for calibrationpurpose, for instance of an engine (or engine control software). Theapplication software may (at least partially) be executed on the device1 or processor 1 a. In other words, for instance software forcalibrating an engine is performed within the device 1 or by theprocessor 1 a which outputs control parameters for an engine. In areal-world scenario, the access times to a first memory location 5 andto the second memory location 7 may differ. Since oftentimes the firstmemory location 5 or target memory 6 is a Flash-type memory and thesecond memory location 7 or the overlay memory 8 is a SRAM-type memory,the access times may differ due to the different access times due todifferent physical properties. This results in different read-out timesof first and second memory locations 5, 7 from the memories 6, 8. Alsothe read-out time of the memories 6, 8 and of the first and secondmemory locations 5, 7 may differ due to contention when accessing amemory. For instance, multiple devices 1 may try to access one memorylocation 5, 7 or one memory 6, 8, meaning the same memory 6, 8 at atime, elongating the read-out time of the respective memory location 5,7or memory 6, 8. Also, contention may occur by multiple-access to a busto which the memories 6,8 are coupled.

The device 1 may contain a processor 1 a processing the data from thetarget memory 5 or from the overlay memory 7 being read-out by thedevice 1. Since the data can, in most cases, be read-out by the device 1or processor 1 a quicker from the overlay memory 8 than from the targetmemory 6, the processor 1 a may, in a conventional system, potentiallyprocess the read-out data earlier than it is supposed to do. This maylead to wrong data processing within the processor 1 a since processingoccurs too early. Ultimately, this may result in a complete failure, forexample if some timing assumptions in the software may be violated.Alternatively, the software may run fine in a development mode, when afast memory (for example the memory 8) is used, but fail in a realapplication scenario when a slower memory (for example the memory 6) isused, which would render the development mode unreliable.

Hence, the overlay mechanism 4 or the corresponding method foroverlaying data may assign to each target address range a target accesstime. According to the disclosure the real time performance of theoverlay system may be improved by modifying the timing behavior of theoverlay system. This may work as follows: The target access time maydescribe the expected number of cycles required to perform an access ortarget access from the processor 1 a. When an overlay translation isperformed the actual number of cycles required to access the overlaymemory 8 are counted. If the real number of cycles taken for the access(for example, of the overlay memory 8) is less than the target accesstime, the processor 1 a is stalled by the difference in the number ofcycles. This allows additional cycles to be added to the access time forthe overlay memory 8 to give access time as would have been seen fromthe target memory 6. Hence, according to the disclosure the real timeperformance of the overlay system is improved by modifying the timingbehavior of the overlay system. So according to the disclosure not onlythe problem of data table location is solved by also the problem of dataaccess times. This is of interest since in a real-time system the accesstime of the data is critical. Real time consideration may be of interestsince switching the data tables from (potentially slow) flash to(potentially fast) SRAM changes the real-time behavior of the system.This may cause unwanted effects.

So, in this manner it may be prevented that data being stored in theoverlay memory 8 is read-out before (or faster than) data could beread-out in the target memory 6. In result, it is avoided that that thedevice 1 or the processor 1 a receives and processes data before it isready to read-out data. Also, the processor 1 a may, for example, obtaindata approximately with the same delay, irrespective of whether adevelopment mode (memory overlay) is used or not. This means that in thesignal path from the overlay memory 8 to a device 1 or to the processor1 a the overlay mechanism 4 prevents that the forwarding of data occursbefore the device 1 or processor 1 a is ready to do so (or faster thanin a case in which the target memory is used). In reality, the overlaymechanism 4 may be part of the device 1 or of the processor 1 a, or maypartially be part of the device 1 or processor 1 a. In that case theoverlay mechanism 4 may—for example—prevent forwarding to that part ofthe device 1 or of the processor 1 a doing the further processing. Inother words, the hardware within the processor/device 1 a, 1 or in thesignal path even before the processors device 1 a, 1 responsible for theoverlaying of data may delay, or prevent for some time, a forwarding ofdata read-out from the overlay memory 8 to other parts of the processor1 a and/or the device 1 not involved in overlaying of data but doingregular computing or processing.

According to a potential modification, the delay of the overlaymechanism 4 of the devices 1 can be configured to compensate at leastpartially for a difference between access time of the first memorylocation 5 and the second memory location 7. Also the correspondingmodification in the method comprises that the time of delaying access orthe target access time is chosen to compensate at least partially anaccess time difference between accessing the first memory location 5 andaccessing the second memory location 7.

By this feature, the difference in access times may be at leastpartially compensated. An access on data to the second memory location 7by means of the overlaying mechanism 4 is delayed so that an access onthe second memory location 7 is more likely to be completed when adirect access of the device 1 to the first memory location 5 would becompleted. At least it may be achieved that the reduced access time onthe second memory location 7 which might be a SRAM-type memory, comparedto the access time of the first memory location 5, which might be aFlash type memory, is at least partially compensated. Due to thisfeature it may be attained that an access to a second memory location 7via the overlay mechanism 4 is postponed or delayed for a certain timerange or delay.

In a real-world scenario, the access time of the first memory location 5may vary, so that a shorter access time to the first memory location 5is possible, shorter than the mean access time to the first memorylocation 5. In other words, the access time to the first memory location5 may be random in nature with a certain average. The more the inputsignal coming to the requesting device 1 or processor 1 a via theoverlay mechanism 4 or the overlay method is delayed to the mean accesstime of the first memory location 5, the more “realistic” access timesare reached in the case of an overlay situation. Thus, the device 1 maybe “ready” to deal or cope with that input. A device 1 or processor 1 amay, for example, be considered ready to deal or cope with an input ifan access time on a memory location 5, 7 has passed. Typically, anapplication software is running or cooperates with the device 1 orprocessor 1 a. The access of the application software to the targetmemory 6 or the first memory location 5 is typically (or at least insome situations) random in nature. However, in general for randomaccesses on the second memory location 7, which may be a RAM or SRAMmemory, a quicker access is possible than on the first memory location 5or target memory 6, which may be Flash. So by this feature the stabilityof the processing operation may be enhanced as signal input from thesecond memory location 7 may occur more likely when the requestingdevice 1 or processor 1 a can process the input signal or when the inputsignal would “normally” arrive (in the absence of an overlay). Theaccess time may comprise signal propagation, basic logic operations andthe time required to read out (physically) a memory location 5, 7.

In other words, by delaying the access time to the second memorylocation 7 by the overlay mechanism 4, it is attained that an input ofdata to the device 1 or partitions of the device 1 occurs, when thedevice 1 or partition of the device 1 is ready to deal with said input,or when said input would normally arrive in the absence of an overlay.So the real-time behavior of the system is not changed by overlayingdata from the first memory location 5 to the second memory location 7,wherein typically the second memory location 7 allows a quicker accessthan the first memory location 5. For the above discussed reasons, in areal-time system the access time of the data is critical, andimprovements can be achieved by adapting the access time in the case ofmemory location overlay when compared to a case without memory locationoverlay.

According to another aspect, the overlay mechanism 4 may be configuredto redirect an access to a first target memory range 2 in the firstmemory location 5 to a first overlay memory range in the second memorylocation 7. Also the overlay mechanism 4 may redirect an access to asecond target memory range to a second overlay memory range. The overlaymechanism 4 may be configured to apply a first delay in case of anaccess to the first target memory range and to apply a second delay,which is different from the first delay, in case of an access to thesecond target memory range in case of a redirection. By thismodification, data accesses directed to the first or second targetmemory range may be redirected to a first or second overlay memory rangeof the second memory location 7.

The first or second overlay memory ranges, to which the data may beredirected, may have different access times. Also the first or secondtarget memory range may have different access times. Typically to atleast some degree the access times are random in nature. For instancethis means the application software access to the target memories 6 maybe typically random in nature. In general random accesses on SRAM areexpected to be faster than on a Flash. The different access times may beconsidered by the overlay mechanism 4 and also by the correspondingmethod for overlaying data. Thus, the overlaying mechanism 4 maycompensate the different access times. In other words, since the accesstime to each of the first and the second memory range may be adaptedindividually to the access time of the respective first and secondtarget memory range, a specific adaption on expected access times ispossible.

According to another aspect, the overlay mechanism 4 is configured toextend an access time to the second memory location 7 to be equal to orlarger than a target access time in case of a redirection. By thismodification it may be attained that an access time of a second memorylocation 7 takes at least a minimum time. In other words, the dataarriving at the device 1 upon request (for example, a data read request)from the second memory location 7 are not processed by the device 1 or aprocessor 1 a of the device 1 “too early”, which would lead to a wrongprocessing or at least to a distortion of a real-time behavior (since,for example, an input signal with wrong data may be considered since thedata arrive too early). This modification may especially be applied, ifthe respective data input to the processor is extremely critical. Inother words, specifying a minimum delay may be useful to avoid in anycase that the content or data in a memory location or range arrive tooearly at the processor 1 a and thus, the processor 1 a produces a falseoutput, which may have severe consequences. In this context, “too early”means before a requested input from a first memory location or targetmemory 6 would be expected.

According to an aspect, an access time to the first memory location 5may be longer than an undelayed access time to the second memorylocation 7. The target access time may be equal to or larger than theaccess time of the first memory location 5. Thereby, it is attained thatan access to the second memory location 7 takes at least as long as anaccess time that would be expected if the device 1 intends to access thefirst memory location 1. Therefore, for the target access time a minimumtime corresponding to the access time to the first memory location 5 maybe defined. Thereby it may be ensured that a request by the processor 1a, which is redirected to the second memory location 7 and which may forexample provide data previously processed or buffered by the overlaymechanism 4, may not be fulfilled or completed by the device 1 beforecorresponding data stored in the first memory location 5 would beavailable.

According to another aspect, the target access time may be programmable.This may be done by a user (or a user-provided software) defining avalue in a user accessible register of the device 1. Thereby a user mayspecify this value such that real-time critical parameters, for instancewhen calibrating an engine by the device 1, may not be accessed by thedevice 1 (or by the processor 1 a) earlier than expected. Also by thisenhancement a security buffer in time may be considered when specifyingthe programmable target access time.

According to further aspect of the overlay mechanism 4, the overlaymechanism 4 may be configured to start or initialize an incrementing ordecrementing counter in response to a detection that an overlayoperation is performed. This is a possible realization of an additionaldelay that can be realized by stalling (or delaying) the point at whicha “data valid” is seen at the processor Load-Store unit (or provided bythe overlay mechanism). Also the overlay mechanism 4 may be configuredto signal data received from the second memory location 7 as beingavailable for a processor 1 a in response to a detection that apredetermined number of clock cycles has elapsed since the starting orinitializing of the counter. By using this concept, an easyimplementation may be realized. In case of a decrementing counter, onlywhen the counter is at zero the data may be seen as valid and availableto the device 1 or the processor 1 a to be further processed orforwarded in a processor pipeline. Also by using this enhancement atiming compensation between different memory accesses is realized.

If the overlay mechanism 4 is optionally extended to cover both code anddata access, this overlay mechanism 4 may potentially be useful incompensating for timing differences associated with Flash-to-Flashoverlay as required by various software-over-the-air (SOTA)implementations.

According to an optional enhancement, the target and overlay memory 6, 8or the first and the second memory may be the same memory. In this case,the overlay mechanism 4 may be used to add additional delay cycles toevery access from the memory. This may be used for tuning performance orpower consumption.

Further, by using this enhancement, the overlay mechanism 4 may beemployed within the area for duplication for locksteped implementations.This may support safe operation of the delay timer.

So by using the overlay mechanism 4 and the corresponding method asdisclosed, a programmable delay is possible which allows to compensatefor the timing difference between memory accesses 2, 3 to differentmemory ranges during data access overlay.

In FIG. 3 an example of how overlaying works is illustrated using atable with different accessing and delaying or stalling times. In theleft column, the different target memories 6 are specified. In thisexample the different memories are named Flash-1, Flash-2 or Flash 3.They may be a Flash-type memory, but in principle they could also be aSRAM-type or other memory type, like, for example, a ROM, a PROM, anEPROM, or the like. The three different memories or memory locationsFlash-1, Flash-2 and Flash-3 may be physically in the same target memory6 but they can also be in different target memories 6. In this example,the target memory 6 may correspond to the first memory location 5 butalso the first memory location 5 may be a part or a range of the targetmemory 6. The Flash-1, the Flash-2 or the flash 3 may have differenttarget access times. The target access times may be measured ordescribed in terms of processing cycles of a processor 1 a of the device1 doing the overlaying or by the device 1 doing the overlaying, or onterms of bus cycles. In this illustrated example the Flash-1 has atarget access time of 12 cycles (processor cycles or bus cycles), theFlash 2 has a target access time of 15 cycles and the Flash-3 has atarget access time of 21 (measured in cycles). Since the first memorylocation 5 is at least part of the respective target memory 6,corresponding statements apply for the first memory location 5 and forthe target memory 6 (sometimes also designated as “first memorylocation”). In other words, a first memory location designates a part ofa target memory or a target memory in its entirety. Similarly, a secondmemory location may designate a part of the target memory mentionedbefore, or a part of another target memory, or the another target memoryin its entirety.

During the overlaying, data (or a data access) is overlaid to a secondmemory location 7 (for example, by means of the mechanism 4 foroverlaying data or by the method for overlaying data). The second memorylocation 7 is at least part of an overlay memory 8 but may also be theentire overlay memory 8. Different “second memory locations” 7 may alsobe in different overlay memories 8. This means the different overlaymemories 8 may not be part of the same memory, for example within anintegrated circuit (IC), or may be, for instance, even an externalmemory just connected by an interface to the IC on which the overlayingmechanism 4 takes place or the overlaying method is implemented.

An overlay access on a second memory location 7 which may be at leastpart of an overlay memory 8 also takes some time. The time may also bemeasured in processing cycles of a device 1 or a processor 1 a doing theoverlaying. In the illustrated table, the overlay access time foroverlaying the second memory location 7 takes a different number ofcycles for each “first memory location” 5 or target memory locationFlash-1 Flash-2 and Flash-3. Namely access to target memory locationFlash-1 takes 10 cycles, access to target memory location Flash-2 takes14 cycles and access to target memory location Flash-3 takes 15 cycles.Apparently, in these examples, accessing the second memory location 7(overlay access time) takes less cycles than accessing the first memorylocation 5 (target access time). Therefore the device 1 or the processor1 a doing the overlaying is delayed or stalled in order to compensatethe time difference between accessing the first memory location 5 andthe second memory location 7. The number of cycles being delayed (i.e.by which an access to the overlay memory is delayed or during which theprocessor is stalled) is the difference between the target access timeand the overlay access time (both measured in cycles). In these examplesthe overlay access time on the Flash-1 (i.e. when the processor requestsaccess to “Flash-1” and the access is overlaid or redirected to a“second memory location” corresponding to “Flash-1”) is delayed(extended) by 2 cycles, the overlay access time on the Flash-2 isdelayed for 1 cycle and the overlay access time on the Flash-3 isdelayed for 6 cycles. By delaying for the said number of cycles anaccess on the respective second memory location, the access is delayedso much that it occurs with a same timing (or even afterwards) whencompared to an access directed directly to the first memory location 5(target access time). In this way, an access of the device 1 or of theprocessor 1 a requesting data from the first memory location 5, which isoverlaid to the second memory location 7, is not possible (or completed)until an access on the first memory location 5 would be possible (orcompleted). Therefore it is avoided that the processor 1 a or the deviceprocesses wrong data and thus, in consequence may produce the wrongoutput.

But in reality also a second scenario is possible (as illustrated in thelower block in FIG. 3). The lower block in FIG. 3 illustrates an exampleof a “Flash-1” first memory location 5. In this case, the target accesstime on the first memory location 5 still takes 12 cycles. But incontrast to the access on the “Flash-1” memory in the previouslydiscussed example, now the overlay access time on the second memorylocation 7 (which is the overlay memory for “Flash-1”) takes 15 cycles.Apparently, now it takes longer to access the second memory location 7in the overlay memory 8 than the processor expects for an access of datastored in the corresponding first memory location 5. The differencebetween the number of cycles when accessing the first memory location 5and the second (overlay) memory location 7 is now 3 but the sign isnegative. In that case, the device 1 or the processor 1 a is delayed orstalled for 0 cycles, as accessing the second memory location 7 (overlayaccess time) takes longer than accessing the first memory location 5(target access time). This is not a problem since even if the overlayaccess time is longer than the target access time it is ensured thatdata is not processed by the processor 1 a or the device 1 too early. Inthis example the algorithm running on the device 1 or processor 1 a istypically implemented to cope with an input arriving somewhat later thantypically expected from the first memory location 5. So there is noproblem for the overlaying method or the overlay mechanism.

Such a scenario is likely to occur if many accesses on the same secondmemory location occur at the same time. In this case an access time tothe second memory location 7 increases significantly, so that an accessis likely to take longer than an access to a first memory location 5.Also such a scenario is likely to occur if the signal path is long orcomprises many obstacles taking time to be passed by a signal. Such anobstacle may be for example a number or bridges on a bus causing a longdelay. Such a long delay may be 5, 10, 15, 25 or more processor cycles.

So, in other words, the overlay memory 8 is not always faster than thetarget memory 6. This depends on where in the system the target memory 6and the overlay memory 8 are relative to the requesting processor 1 aand also on the contention of the target memory 6, the bus system andthe overlay memory 8. The application software access to the targetmemories 6 is typically random in nature. In general, for randomaccesses SRAM is expected to be faster than a Flash. In case where thetarget access time is less than the overlay access time no additionaldelay is added.

In FIG. 4 an entire system for overlaying is illustrated. By means of adevice (D) 1 an overlay mechanism 4 or a method for overlaying data maybe performed. In FIG. 4 a device 1 connects a first memory location(FML) 10 and a second memory location (SML) 11 via bus 9. Thereby bothmemory locations 10, 11 are connected via the same bus 9. The device 1comprises an overlay mechanism 4 which it configured to or configurableto redirect an access which is directed to the first memory location 10to a second memory location 11. Therefore data which is intended by theprocessor 1 a in the device 1 or the device 1 (or by the respectivesoftware) to be stored in a first memory location 10 is stored in asecond memory location 11 instead. So it may be avoided to wear-out thefirst memory location 10, since the information is stored instead in thesecond memory location 11. The access time of data being stored in thesecond memory location 11 might differ from the access time of databeing stored in the first memory location 10.

In other words, rather than re-writing the flash-memory (for example,the first memory location 10) at every data table change, the datavalues may be placed in a SRAM (for example, at the second memorylocation 11). Rewriting a flash may be time consuming and may lead to aflash wear-out. Typically the first memory location 10 may beimplemented as a flash and the second memory location may be implementedas a SRAM.

In FIG. 4 the delay is added on the side of the device 1 of the bus 9.It is better to add the delay there than (centrally) at the overlaymemory 8, which may comprise the second memory location 11. This issince the overlay memory 8 has no idea of how far away the requestingprocessor is in the system or which target 6 (which may comprise thefirst memory location 10) it is overlaying so it can only provide an“average” delay unless a complex delay system was incooperated. Thiswould require additional information being provided over the bus 9 toidentify the overlay operation being performed.

Providing the mechanism (for example, the overlay mechanism describedherein) at the processor 1 allows re-use of current overlay logic. Inprinciple about any SRAM may be used in the system as an overlay memory8 (DSPR, PSPR, LMU, DLUM, EMEM). Implementing the delay logic (withinthe overlay mechanism 4) at the requesting node (processor 1 a) ratherthan at the SRAM (overlay memory 8 or second memory location 11) leadsto a simpler system.

The access time on the second memory location 11 may be reduced. Thismay be caused by a lower number of contentions on the second memorylocation 11 than on the first memory location 10. For instance if onedevice 1 in the system often requests data from the same first memory(comprising, for example, memory location 10) it may have asignificantly increased response or access time. In principle, the sameapplies (speaking of contentions) to any other memory, other than thememory comprising the first memory location 10, including the memorycomprising the second memory location 11.

Also the first and the second memory location 10, 11 may be a differenttype of memory. For instance, the first memory location 5, 11 is aflash-type and the second memory location 7, 11 is a SRAM type. Hence,the access time due to the different physical properties may also bedifferent since a flash-type memory has a shorter access time than anSRAM-type memory.

According to a further aspect, the overlay mechanism 4 can be configuredto adapt the delay depending on (known or estimated) access times ofmemory locations 10, 11. The overlay mechanism 4 and/or thecorresponding method may detect if a second access to the first memorylocation 10 follows (for example, in terms of a memory address to beaccessed) on a first access to the first memory location 10, causing achanged access time to the first memory location 10 when accessingsuccessional memory locations of the first memory location 10. This mayresult in the changed access time being shorter than the time of thefirst access to the first memory location 10. In this case the delay(applied when performing memory overlaying) can be adapted to thechanged access time of the first memory location 10 when accessing thesecond memory location 11. So the shorter access time when accessing thesecond time (in succession) may be compensated.

In many real scenarios, a device 1 which may comprise a processor 1 amay request for data being successional (for example, at directlysubsequent memory locations), concatenated or associated in a memorylocation 10, 11. Therefore, in such a scenario, successional,concatenated or associated memory locations within a memory 10, 11 canbe accessed quicker by the device 1 (for example, starting from thesecond access on the memory location 10, 11 of a sequence ofsuccessional accesses).

For instance associated, concatenated or successional memory locations5, 7 may by loaded into a prefetch buffer of the first memory location 5in response to a first access on the memory location, thus allowingquicker access on the data stored in the prefetch memory. The device 1may be aware of this changed access time. The changed access time (forthe second and further successional accesses) is typically shorter thanthe access time for the first time access to the memory location.Therefore, the program running in the device 1 or in the processor 1 acan expect an input earlier if an associated, concatenated orsuccessional memory location 10, 11 is accessed by the device 1 or bythe processor 1 a. So the delay of the overlay mechanism 4 and of thecorresponding method may be adapted to the earlier input. The delay ofthe overlay mechanism 4 may elongate the access time to the secondmemory location 11 to the access time of the first memory location 10 ormay add a delay to the access time to the second memory so that thedelay and the access time to the second memory 11 together are a longertime than the access time on the first memory location 10.

According to an aspect, the device 1 may be connectable or may beconnected to the first and second memory location 10, 11 by at least onebus 9. By means of a bus 9, a communication in a defined, known orpredictable manner is possible since a bus may provide a well-testedexchange of signals or data. However, some uncertainties of the accesstime may also arise, for example in the case of contention.

According to another aspect, the overlay mechanism 4 may be configuredto compensate for varying un-delayed access times to the second memorylocation 7. When accessing a real memory (for example, the second memorylocation), the required time may vary statistically. An overlaymechanism 4 according to this modification may compensate suchstatistical varying access times to the second memory location 7.

The embodiment illustrated in FIG. 4 can be combined with the deviceillustrated in FIG. 1. In that case, the accesses directed to the firstmemory location 2 and the accesses directed to the second memorylocation 3 shown in FIG. 1 employ both the (same) bus 9 in FIG. 4 inorder to access the first and second memory locations 10, 11. In otherwords, memory location 10 corresponds to memory location 2, and memorylocation 11 corresponds to memory location 3.

Also, the embodiment illustrated in FIG. 4 can be combined with theembodiment illustrated in FIG. 2. In that case the bus 9 corresponds tothe data access (line) 19. The first memory location 10 corresponds to asection of the target memory 6 or to the entire target memory 6 and thesecond memory location 11 corresponds to a section of the overlay memory8 or to the entire overlay memory 8. The section of the target memory 6may be equal to the first memory location 5 in FIG. 2. The section ofthe overlay memory 8 may be equal to the second memory location 7 inFIG. 2.

In FIG. 5, a further embodiment is illustrated. In principle itcomprises the same components as already described in FIG. 4, forinstance, a device 1, a bus 9, a first memory location 10 and a secondmemory location 11. Accordingly, reference is made to the description ofthese components and their interaction in FIG. 4. The details regardingthe interaction of the components as described when discussing acombination of FIG. 1 and FIG. 4 or FIGS. 2 and 4 also apply.

In FIG. 5 it is illustrated that more than one of one instance ofcomponents 1, 10, 11 may be employed and that multiple components mayrely on one (shared) bus 9. For instance several (for example, between 2and 10) devices 1 rely on one bus 9. Also in principle several (forinstance between 2 and 10) first memory locations 10 and/or secondmemory locations 11, may access or employ one bus 9. So, a typicalsystem may contain or comprise multiple processors 1 a, multiple flashmemories and/or multiple overlay memories, which may, for example, becoupled via one bus, or via different segments of a bus. Using thismechanisms, each processor's overlay operation may be separatelyadjusted for its view of the flash and overlay memory access times.According to the disclosure, different target access times are allowedto be defined for each target range and hence for each flash memory. Thefirst memory locations 10 may, be but do not have to be, of one giventype of memory. For example, a flash type memory may be used for thefirst memory locations 10. Also the second memory locations 11 may be,but do not have to be, of one given type of memory. Nevertheless, aSRAM-type memory may be used for the second memory locations 11. Inprinciple the first memory location 10 and the second memory location 11might be a SRAM-type or a Flash-type memory.

In principle, also one memory (which may be a SRAM-type or flash-typememory) may serve jointly as a first memory location 10 and a secondmemory location 11. In this case different sections or ranges of thememory serve for different purposes, one as a first memory location andthe other one as a second memory location. However, it is preferred thatthe first memory location(s) and the second memory location(s) usedifferent types of memory (having different access times).

In such an embodiment as illustrated in FIG. 5 contentions whenaccessing a memory location 10, 11 or memory 6, 8 are likely to occur.This is due to the multiple number of “actors”, especially devices 1,all requesting data from memory locations 10, 11. This may occur(almost) jointly, meaning almost in a time-parallel manner. Therefore ahuman user programming the algorithms or programs running on a device 1can estimate—due to his experience and due to his knowledge of thetopology of the bus 9 and of the actors—how long an expected access timeon a first memory location 10 is likely to be. Therefore a human usercan provide to the overlaying mechanism 4 or to the method foroverlaying data an input (for example, by inserting a configurationinstruction into a software portion) how long it takes for a certaindevice 1 (incorporating or cooperating with an overlay mechanism 4) toaccess a first memory location 10. Also, a user may chose for securitycritical applications an expected access time to be so long that thedevice 1 can access the first memory location 10 in any case, forexample with a probability higher than 99% or 99, 9%. Therefore, it isensured or guaranteed that the device does not operate faster in thecase of a memory overlaying when compared to an operation without amemory overlaying. This is due to the long access time for theoverlaying situation which may be specified by the user. The access timefor the overlaying situation may be defined by the programmable delay.

However, within the scope of this disclosure the access time could alsobe fix-programmed (unchangeable by a user). In that case, it may bespecified by the device manufacturer how long it typically takes foraccessing the first memory location 10. This may be suitable if a personskilled working with such system does not have enough knowledge aboutthe access times to be expected.

A third option would be that a default access time for accessing thefirst memory location 10 is programmed. This default value may bechanged by a user for special purposes. Such a default access time maybe useful in order to ensure a working system without too manymodifications in an early testing stage, for example when calibrating anengine (or when designing and fine-tuning an engine control software).In case later on during calibration more specific knowledge is availableand also more resources are available to consider details duringcalibration (fine-tuning), the default access time of a first memorylocation 10 may be adapted.

According to this disclosure it is also possible to mix the threedifferent options for different parameters or data, which may beintended by the device 1 to be stored on the first memory location 10.

In principle according to this disclosure such features are alsopossible for the embodiments illustrated in FIG. 4. Nevertheless theywill rather be applied in a system with multiple components 1, 10, 11,as in such a system access times are more complicated to determine.

FIG. 6 illustrates a further embodiment teaching a system with differentsegments 9 a, 9 b, 9 c, 9 d of the bus 9. The segments of the bus 9 a-9d each comprise one or more bus lines. The bus lines may beuninterrupted within one segment 9 a-9 d. The different segments are(partially) connected to each other by at least one bridge 12. In theexample, the bus segments 9 a, 9 b, 9 d are connected by one bridge 12.The bus segments 9 a, 9 b, 9 c are connected in series by two bridges12. The bus segments 9 a, 9 b, 9 c are electrically connected asenumerated. In principle (although not illustrated) a circular-design ofbus segments 9 a-9 d is also possible within this disclosure. Thebridges 12 may, for example, be clocked by a common clock signal 14originating from a common clock 13. In summary the bridges 12 may servefor an exchange of signals or data between bus segments 9 a-9 d and mayalso serve for a (time-) synchronization of bus segments 9 a-9 d.Nevertheless the bridges 12 cause an unintentional delay which maycontribute significantly to the transmission time over the bus 9,meaning from one component 1, 10, 11 in a first bus segment 9 a-9 d to asecond component 1, 10, 11 in a different bus segment 9 a-9 d.

A bus segment 9 a-9 d may comprise (or may be directly coupled with) atleast one of a device 1, a first memory location 10 and a second memorylocation 11. For instance, the illustrated bus segment 9 a accesses (orconnects) a device 1, and three different first memory locations 11. Thebus segment 9 b accesses or connects three devices 1, one first memorylocation 10 and a second memory location 11. The bus segment 9 caccesses or connects exclusively first and second memory locations 10,11 but does not comprise a device 1. Thus, in case the memory locationsin segment C or bus segment 9 c are accessed, this can only occur bydevices 1 being in other bus segments 9 a, 9 b, 9 d. The illustrated bussegment 9 d comprises a device 1 and three second memory locations 11.In principle a device 1 in a first bus segment 9 a-9 d can also accessmemory locations 10, 11 in other bus segments 9 a-9 d. This may dependon availability of memory resources or may make sense for duplication ofdata storage. For instance in case one segment A-D is damaged (forexample by ESD or semiconductor degeneration over time), data may bestored in other segments A-D. This may especially apply if one segmentA-D is an external segment. External means, in this context, not being abus segment being part of one chip but being externally connected by aninterface (which may comprise a bridge 12) to the chip comprising atleast some of the other segments A-D or bus segments 9 a-9 d.

The “signal delay by purpose” (which is applied in the case of anoverlaying operation) occurs on the side of the device 1, not on theside of the memory location 10, 11 being the overlay memory 8 to which adata access is redirected. Indeed, it is applied by the overlayingmechanism 4 of the device 1. The second memory location 11 (or theoverlay memory 8) has no idea (does not possess the information) of howfar away the requesting device 1 or processors 1 a is in the system orwhich first memory location 10 or target location or target memory 6 itis overlaying. So, if there was a delay being implemented on the side ofthe second memory location 11 or on the side of the overlay memory 8,only an average delay or another (common) delay, for example being themaximum expectable delay, could be used easily (without additionalsignaling efforts). This problem could only be circumvented by a complexdelay system if a delay at the side of the memory was used. Such acomplex delay system would possibly provide the information about thedelay the device 1 or processor expects for a respective first memorylocation 10 or a target memory 6 to the second memory location 11 or theoverlay memory 8. In that case, the second memory location 11 or theoverlay memory would be able to perform the delaying of access to thesecond memory location 11 or overlay memory 8 by a respective processor1 a or device 1.

Providing the overlay mechanism 4 or delay mechanism at the processor 1a or at the device 1 (or at least at the side of that components) allowsthe re-use of the (current) overlay logic. In principle for instance foran overlay memory 8 or a second memory location 11 any SRAM in thesystem may be employed. This system comprises different memory regionsor memory types, for example designated as DSPR, PSPR, LMU, DLMU and/orEMEM in some embodiments. Implementing the delay logic at the processor1 a or at the device 1 (generally speaking at the requesting node)rather than at the overlay memory 8 or at the second memory location 11(possibly a SRAM) may lead to a far simpler system.

The previously discussed system may optionally comprise additionalpossible features, modifications or enhancements.

In an embodiment, the bus segments 9 a-9 d may be coupled via one ormore bridges (B) 12. The memories 10, 11 may be coupled with differentsegments 9 a-9 d of the bus structure 9. A first device 1 or a firstprocessor 1 a and a second device 1 or a second processor 1 a may becoupled with different segments 9 a-9 d of the bus structure 9. Thememories 10, 11 may comprise target memory ranges (which may, forexample, be used during a “normal” program execution) and overlay memoryranges (which may, for example, be used during a program development orprogram tuning operation). A relationship between an access time of thefirst processor 1 a to a target memory range associated with anoperation of the first processor 1 a and an undelayed access time of thefirst processor 1 a to an overlay memory range associated with theoperation of the first processor may be different from a relationshipbetween an access time of the second processor to a target memory rangeassociated with an operation of the second processor and an undelayedaccess time of the second processor to an overlay memory rangeassociated with the operation of the second processor. A delay of theoverlay mechanism 4 of the first device and a delay of the overlaymechanism 4 of the second device may be programmable individually andmay allow a compensation of the different relationships between accesstimes to target memory ranges and corresponding overlay memory ranges.

By this feature a user or human user who knows the system architectureand system characteristics can react on requirements by specifyingindividual delays for different processors or different delay for thefirst and the second processor (for example, using configurationinstructions included in a code). For instance, the number of bridges 12in the signal path over the bus 9 between a first or second device 1,which may comprise a processor 1 a, and at least one of a first andsecond memory location 5, 7 may differ. Since a bridge 12 has asignificant effect on signal delay or signal propagation time on bus 9,the number of bridges 12 in the signal path influences the access timeof a device 1 including an overlay mechanism 4. Also, a user mayestimate the number of signal contentions from the view of a device 1.For instance, a user may consider that a device 1 may access a memorylocation 10, 11, while one or more of the other devices 1 may access oneother memory location 10, 11. In such a scenario, the one or more otherdevices 1 accessing the other memory location 10, 11 may cause some buscontention when accessing the memory locations 10, 11. Therefore, whenprogramming a delay for the overlay mechanism 4, the user may program alonger delay time since a long access time may be expected when thedevice 1 may intend to access the first memory location 10. This may becaused by either or both the number of bridges 12 in the pathway or thecontentions expected when accessing the memory location 10, 11.

In other words, an actual difference (or actual average distance, orestimated actual difference) between access times to a target memoryrange and to an overlay memory range may be considered by a user whenprogramming a delay for the overlay mechanism. One delay component maybe determined by the architecture of the bus system or bus systems,wherein a number of bridges between a given processor and a physicalmemory comprising the target memory range may be different from a numberof bridges between the given processor and a physical memory comprisingthe overlay memory range. Furthermore, contention-based delays may bedifferent for an access to the target memory range and for an access tothe overlay memory range. Thus, the delay for the overlay mechanism maybe programmed individually on the basis of a knowledge of the locationof the respective processor within a bus system, a knowledge of thephysical memories involved within the bus system, and an known orestimated delay impact caused by bus contention or other factors.

Thus, by using such a system comprising a bus system with bus segments 9a-9 d, an individual access time of a device 1 to a second memorylocation 11 (and also to a first memory location) can be taken intoconsideration. The access time of devices 1 to the second memorylocation 11 may differ, since, for instance, the signal path from afirst device 1 to a corresponding second memory location 11 may differfrom a signal path from a second device 1 to a corresponding secondmemory location 11. For instance there may be a different number ofbridges 12 in the signal path of a bus 9 or bus system, or the accesstime from a device 1 to a corresponding second memory location 11 maydiffer from the access time from another device 1 to a corresponding(other) second memory location 11 since there are a different number ofcontentions on the signal path to be considered. For instance, when thefirst device 1 in segment A accesses a (corresponding) second memorylocation in segment C, two bridges 11 have to be passed since the onlyway is crossing segment B. In contrast, an access of device 1 in segmentB is not delayed by the bus architecture when accessing a first orsecond memory location 10, 11 in segment B. However, when a device 1 insegment B is trying to access a second memory location 10, 11 in segmentC, the access is delayed by one bridge 12. So, the access time for adevice 1 to a first or second memory 10, 11 depends on the one hand onthe signal path and on the other hand on the number of contentions onthe bus 9 when accessing a memory 10, 11 location. Also the physicaltype of the memory location 10, 11 contributes to the access time.

So, the access time of an overlay memory 8 (which may by a second memorylocation 11) as seen from the processor 1 a (which may be part of adevice 1) may not be a constant due to contention at the bus system 9and the overlay memory 8. The use of a variable delay on the returningdata provides a degree of compensation for this contention. Therebyreturning data may be the data being requested by the processor 1 a ordevice 1 in the bus system 9. The returning data may be stored in theoverlay memory 8 or the second memory location 11.

In FIGS. 7a-7b two different options are illustrated how the delay mightwork. In FIG. 7a , there is an internal delay unit 18 being part of thedevice 1 performing the overlay mechanism 4. Before an input signal(which may be a response of a memory read request) is allowed to passfrom the bus 9 to a processor core, it is delayed by a delay unit (IDL)18. The bus 9 may also be a bus segment 9 a-9 d as discussed in FIG. 6.In other words, parts of the device 1 may function as an overlaymechanism 4 which comprises a delay unit 18. This may be implementedwithin a processor 1 a being part of the device 1 (or forming thedevice). In that case the delay by the delay unit 18 may be realized byskipping or stalling some cycles of the processor 1 a before the signalcoming in from the bus 9 is forwarded to further part of the processor 1a not being involved in the delay (for example, to a processor core). Inthis implementation the delay unit 18 is also part of the processor 1 a.

According to another option, there is an external delay unit 17 asillustrated in FIG. 7b ). This means the delay unit (EDL) 17 is not partof the device 1 but forms an interface between the device 1 and the bus9 or bus segment 9 a-9 d. In other words, the device 1 comprises anoverlay mechanism 4 configured to or being configurable to redirect anddelay access to a second memory location 3. For example, the delay unitmay delay the data read from the overlay memory location, and/or a “dataready” signal.

The overlay mechanism 4 outputs to the delay unit 17 an informationdescribing by how much a requested signal (for example read data) fromthe second memory location 11 is to be delayed. The “signal” typicallycomprises data which was stored in the second memory location 11.

In an example, a delay to be applied by the delay unit may beprogrammable. For example, the processor may write a delay value to a“special function register” (for example, using one or more programinstructions), and the delay value stored in said special functionregister may determine the delay to be used by the delay unit.

Alternatively the delay unit 17 might, for example, obtain a delayinformation or a delay value from the device 1, which is specified bythe device 1 in a fixed manner or which is specified by default withinthe device 1. In contrast to the solution in FIG. 7a ) an additionalcomponent, namely the delay unit 17, may form an interface.Nevertheless, in this case, the device 1 does not need to provideresources as, for example, processing time or hardware resources, forthe delay.

According to another aspect, the device 1 may comprise a processor 1 a.The method for overlaying data or the overlay mechanism 4 may delay aprocessing operation of the processor 1 a requesting access to the firstmemory location 10 or may delay a forwarding of data from the bus 9 tothe processor 1 a, to thereby delay access to the second memory location11.

The processor 1 a in the device 1 may request for data being stored in afirst memory location 10. Since the access to data being stored in thefirst memory location 10 may be redirected by the overlay mechanism 4 tothe second memory location 11, the access (or the effective access time)of the processor 1 a to the second memory location 11 needs to beprolonged before the data is further processed in the processor 1 a,which is attained by this modification. According to the a first optionof this modification, this may be realized by delaying a processingoperation of the processor 1 a. For example by internal slow-down orhalting of the processor 1 a itself, a prolongation of access time onthe second memory location 11 is attained. The first option may beimplemented by an overlay mechanism or a method for overlaying datawhich may be delaying a processing operation by stalling at least onecycle of the processor 1 a. According to this option, the delay may beachieved by the processor 1 a itself. In other words, parts of theprocessor 1 a or device 1 work as a delay unit 18. This may be possiblewithout other functional units coupled to the processor 1 a or overlaymechanism 4 for the purpose of delaying. According to the second optionof this modification, a delay may be realized by delaying a forwardingof data from the bus 9 to the processor 1 a. This may occur by means ofa delay unit 17 which may be at an interface of the bus 9 and theprocessor 1 a.

In principle both devices 1 and delay units 17, 18 as illustrated inFIG. 7 can be combined with any other aspects and embodiments beingdiscussed in this disclosure.

FIG. 8 illustrates a flow chart how an overlay mechanism 4 or a methodfor overlaying data according to an embodiment may, for example, work.

There are two steps illustrated: In the first step S1, an access whichis directed to a first memory location 10 is redirected to a secondmemory location 11. The second step S2 involves a selective delaying ofan access to the second memory location 11 in case of a redirection by atime.

In the first step S1, data is stored in a second memory location 11.This may be done by the overlaying mechanism 4 being part of the device1, as discussed previously. Therefore data which is intended to bestored by the device 1 or processor 1 a in a first memory location 10 isstored in the second memory location 11 instead. So a wearing-out of thefirst memory location 11 is prolonged. Since the first memory location10 oftentimes has a longer access time than the second memory location11, data being stored in the second memory location 11 instead of thefirst memory location 10 can be accessed quicker. In some cases, thedevice 1 requesting for a data access to the first memory location 10(which is redirected by the overlay mechanism 4 or method to the secondmemory location 11) is not ready to process such an input signal ormight produce a wrong output since the input signal is processed tooearly, or a result of the processing may not represent a “real world”result which would be obtained without a redirection. Therefore anaccess to the second memory location 11 is delayed selectively (step S2)in case of a redirection, in order to avoid this problem. This occurswithin the device 1 or in the signal path from the second memorylocation 11 to the device 1 directly before the device 1.

According to the disclosure all the aspects, embodiments, features orthe like can be combined. According to the disclosure, all components,comprising the devices 1, processors 1 a, busses 9, bus segments 9 a-9d, bridges 12, first memory locations 10, second memory locations 11,target memories 6 and/or overlay memories 8 may be on one single chip.Nevertheless they may also be on different chips. Also the chip mightinclude at least the processor 1 a or device 1 and other components, butat least one of the memories 6, 8 or memory locations 10, 11 might beexternal. This may be especially suitable for data duplication.

Conclusions

The disclosure refers to an overlay mechanism or method redirecting dataload access from a first memory location to a second memory location.Such a mechanism called data access overlay can be used by a customerduring product development stage. Such a mechanism can be employed whencalibrating an engine management system. In such a calibration system adata table that resides in the flash memory can be tuned. This mayinvolve frequent modification to the table values. A first memorypossibly may be a flash memory and a second memory may be a SRAM memory.Rewriting the flash memory at every data table change is time consumingand may lead to a wear-out of the first memory, which applies especiallyif the first memory is a flash-type memory. The change in location ofthe data is not visible to the application software but may be performedby hardware within a device or processor under control of thedebug/calibration system. The hardware may contain a programmable tableof target address ranges and an associated set of redirect addressranges to be substituted if a data access is performed to the targetaddress range. The redirect address ranges are SRAM locations and may beany SRAM in a system comprising DSPR, PSPR, LMU, EMEM.

The disclosure discusses a device, comprising an overlay mechanismconfigured or configurable to redirect an access which is directed to afirst memory location to a second memory location. The overlay mechanismis configured or configurable to delay access to the second memorylocation in the case of a redirection.

By such an overlay mechanism it can be attained that a device employs asecond memory location instead of a first memory location. Since thefirst memory location needs not to be employed a wear-out of the firstmemory location can be avoided. Since due to the overlay mechanism thesecond memory location can be employed instead of the first memorylocation, the second memory location can be accessed more quickly fromthe device than the first memory location. In other words, the contentof the second memory location can be read-out more quickly. Thereforethe access to the second memory location may be delayed in order tocompensate this.

Also the disclosure discusses a method for overlaying data. The methodcomprises redirecting an access which is directed to a first memorylocation to a second memory location, and selectively delaying access tothe second memory location in case of a redirection by a time. Delayingmeans in the context of this disclosure an intentional delaying duringsignal or data processing or that a delaying or postponing of signalprocessing occurs by purpose. In other words, the delay according tothis disclosure is different to a parasitic delay which may occur insignal processing in a device, system or chip unintentionally due toside effects of some components. Such a side-effect may by a responsetime of a circuit consisting for instance of transistors like MOSFETs,bipolar transistors and capacities or the like.

In principle the method provides the same advantages as the device.Since an access occurs to data being stored in a second memory location,the data can be accessed more quickly than data being in the firstmemory location. Therefore by the overlay method, which selectivelydelays access to the second memory location in case of a redirection bya time, the access to the second memory location by the devicerequesting access may be delayed or postponed.

Also the disclosure discusses a system comprising a first device asalready mentioned, wherein the first device comprises a first processor;a second device as already mentioned, wherein the second devicecomprises a second processor; a bus structure comprising a plurality ofbus segments; and a plurality of memories. The first processor and thesecond processor are coupled with the memories via the bus structure. Adelay of the overlay mechanism of the first device and a delay of theoverlay mechanism of the second device are programmable individually.

In a device or system design numerous modifications, aspects andfeatures are possible comprising for instance following features andmodifications. Also corresponding features and modifications for themethod are possible.

By all of the aspects, features or the like discussed so far anoverlaying of a second memory location or a flash memory may be possiblewithout impacting a time or real-time behavior of the device or a systemcomprising the device is possible.

To further conclude, some embodiments provide a mechanism to redirectdata load accesses from flash memory to SRAM memory. This mechanism isknown as data access overlay and is typically used by a customer duringthe product development stage when they are calibrating, for example,the engine management systems. In such a calibration system, data tablesthat reside in the flash memory are being “tuned”. This sometimesinvolves frequent modification to the table values. Rather than re-writethe flash memory at every data table change (which is time consuming andleads to flash wear-out), the data values are placed in SRAM. The changein location of the data is not visible to the application software butis performed by hardware within the processor under control of thedebug/calibration system. This hardware contains a programmable table oftarget address ranges and an associated set of redirect address rangesto be substituted if a data access is performed to the target addressrange. The redirect address ranges are SRAM locations and may be anySRAM in the system (DSPR,PSPR,LMU,EMEM)

This system allows the logical translation of addresses withoutmodification of the application software and hence allows the Flash datatables to be “overlayed” by the SRAM. This solution solves the problemof data table location. However, embodiments according to the disclosurealso address the problem of data access times. In a real time system theaccess time of the data is critical. It has been found that switchingthe data tables from (slow) flash to (fast) SRAM should not changes thereal-time behavior of the system.

Embodiments seek to improve the real time performance of the overlaysystem by modifying the timing behavior of the overlay system describedabove. The proposed operation is as follows:

Each target address range is assigned a target access time describingthe expected number of cycles required to perform an access to thememory from the processor. When an overlay translation is performed theactual number of cycles required to access the overlay memory arecounted. If the real number of cycles taken for the access is less thanthe target access time the processor is stalled by the difference in thenumber of cycles. This allows additional cycles to be added to theaccess time for the overlay memory to give the same access time as wouldhave been seen from the target memory.

It should be noted that the access time of the overlay memory as seenfrom a processor will sometimes not be a constant due to contention atthe bus system and overlay memory. The use of a variable delay on thereturning data provides a degree of compensation for this contention.

A typical system contains multiple processors, multiple flash memoriesand may contain multiple overlay memories. Using this mechanism eachprocessors overlay operation may be separately adjusted for its view ofthe flash and overlay memory access times. This proposal allowsdifferent target access times to be defined for each target range andhence for each flash memory.

The proposed system is better than adding delay centrally at the Overlaymemory. The Overlay memory has no idea of how far way the requestingprocessor is in the system or which target it is overlaying so can onlyprovide an “average” delay unless a complex delay system isincorporated. This would require additional information being providedover the bus to identify the overlay operation being performed.Providing the mechanism at the processor (as proposed herein) allowsre-use of the current overlay logic. We can use just about any SRAM inthe system as an overlay memory (for example, DSPR, PSPR, LMU, DLMU,EMEM). Implementing the delay logic at the requesting node (in or closeto the processor requesting to read data) rather than the SRAM leads toa far simpler system.

It should be noted that the Overlay memory is not always faster than theTarget memory.

Rather, this will depend on where in the system the target memory andthe overlay memory are relative to the requesting processor and also onthe contention at the target memory, the bus system and the overlaymemory. The application software access to the target memories istypically random in nature. In general for random accesses we expectSRAM to be faster than Flash. In the case where the target access timeis less than the overlay access time no additional delay is added.

The additional delay can be easily added by stalling the point at whichdata valid is seen at the processor Load-Store unit. The easiestimplementation of the delay counter and delay operation would be to loada decrementing counter with the target access time when an overlayoperation is detected. The counter is decrement by 1 on each cycle untilit reaches zero. Only when the counter is at zero is the data seen asvalid and available by the processor pipeline.

Additional Aspects:

The mechanism described allows for timing compensation between memoryaccesses. If the Overlay system was extended to cover both code and dataaccess this mechanism would potentially be useful in compensating fortiming differences associated with Flash-to-Flash overlay as required byvarious software-over-the air (SOTA) implementations.

In the case where the target and overlay memories are the same memorythis mechanism can be used to add additional delay cycles to everyaccess from the memory. This could be potentially useful for tuningperformance or power consumption.

The overlay system including this proposal is included within the areaof duplication for locksteped implementations. This supports safeoperation of the delay timer.

Embodiments fulfil a customer requirement that they should be able tooverlay flash memory without the system timing or real time behaviorbeing impacted.

A simple embodiment comprises a programmable delay able to compensatefor the timing difference between memory accesses to different memoryranges during data access overlay.

As an alternative, a simple system could be produced that delays alloverlay memory accesses by a fixed amount but this would not have theresolution of this proposal.

In addition, it should be noted that a crossbar circuit may also be usedfor an interconnection between a plurality of processors and a pluralityof memories, for example instead of a bus. The crossbar circuit maycomprise multiple (for example, parallel) data paths, which may be usedto simultaneously to establish multiple connections, each connection,for example, between a processor and a memory. The overlay mechanismmay, for example, be coupled between a processor core and a crossbarswitch (which selectable connects a processor with one out of aplurality of communication paths of the crossbar). The overlay mechanismmay be configured to consider characteristics of the crossbar, like, forexample, possible crossbar contention. In so far, embodiments using acrossbar are similar to embodiments using a bus, or using a bus system(wherein a contention in a crossbar-based system is typically smallerthan a contention in a bus-based system). In other words, the featuresand functionalities described herein with respect to a system using abus also apply to a system using a crossbar, and can be usedindividually or in combination.

The invention claimed is:
 1. A device, comprising: an overlay mechanismconfigured to redirect an access which is directed to a first memorylocation to a second memory location, wherein the overlay mechanism isconfigured to delay access to the second memory location in the case ofa redirection, wherein the overlay mechanism is configured to adapt thedelay depending on access times of memory locations, and wherein theoverlay mechanism is configured to detect if a second access to thefirst memory location follows a first access to the first memorylocation, causing a changed access time to the first memory locationwhen accessing successional memory locations of the first memorylocation, and resulting in the changed access time being shorter thanthe time of the first access to the first memory location, and in thiscase adapting, when accessing the first memory location with the secondaccess, the delay to the changed access time of the first memorylocation, wherein the second memory location is physically separate fromthe first memory location.
 2. The device according to claim 1, whereinthe first memory location is a flash-type memory and/or the secondmemory location is a SRAM-type memory.
 3. The device according to claim1, wherein the delay of the overlay mechanism is programmable.
 4. Thedevice according to claim 1, wherein the delay of the overlay mechanismis configured to compensate at least partially for a difference betweenaccess times of the first memory location and of the second memorylocation.
 5. The device according to claim 1, wherein the device isconnectable to the first memory location and the second memory locationby at least one bus or by at least one crossbar.
 6. The device accordingto claim 5, wherein the device comprises a processor, and wherein theoverlay mechanism is configured to delay a processing operation of theprocessor requesting access to the first memory location or to delay aforwarding of data from the bus or from the crossbar to the processor,to thereby delay access to the second memory location.
 7. The deviceaccording to claim 6, wherein the overlay mechanism is configured todelay a processing operation by stalling at least one cycle of theprocessor.
 8. The device according to claim 1, wherein the overlaymechanism is configured to redirect an access to a first target memoryrange in the first memory location to a first overlay memory range inthe second memory location, and to redirect an access to a second targetmemory range to a second overlay memory range, and wherein the overlaymechanism is configured to apply a first delay in case of an access tothe first target memory range and to apply a second delay, which isdifferent from the first delay, in case of an access to the secondtarget memory range in case of a redirection.
 9. The device according toclaim 1, wherein the overlay mechanism is configured to extend an accesstime to the second memory location to be equal or larger to a targetaccess time in case of a redirection.
 10. The device according to claim9, wherein an access time to the first memory location is longer than anundelayed access time to the second memory location, and wherein thetarget access time is equal to or larger than the access time of thefirst memory location.
 11. The device according to claim 9, wherein thetarget access time is programmable.
 12. The device according to claim 1,wherein the overlay mechanism is configured to compensate for varyingundelayed access times to the second memory location.
 13. The deviceaccording to claim 1, wherein the overlay mechanism is configured tostart or initialize an incrementing or decrementing counter in responseto a detection that an overlay operation is performed, and wherein theoverlay mechanism is configured to signal data received from the secondmemory location as being available for a processor of the device inresponse to a detection that a predetermined number of clock cycles haselapsed since the starting or initializing of the counter.
 14. A device,comprising: an overlay mechanism configured to redirect an access whichis directed to a first memory location to a second memory location,wherein the overlay mechanism is configured to delay access to thesecond memory location in the case of a redirection, wherein the overlaymechanism is configured to adapt the delay depending on access times ofmemory locations, wherein the overlay mechanism is configured to extendan access time to the second memory location to be equal or larger to atarget access time in case of a redirection, and wherein an access timeto the first memory location is longer than an undelayed access time tothe second memory location, and wherein the target access time is equalto or larger than the access time of the first memory location.
 15. Thedevice of claim 14, wherein the overlay mechanism is configured todetect if a second access to the first memory location follows a firstaccess to the first memory location, causing a changed access time tothe first memory location when accessing successional memory locationsof the first memory location, and resulting in the changed access timebeing shorter than the time of the first access to the first memorylocation, and in this case adapting, when accessing the first memorylocation with the second access, the delay to the changed access time ofthe first memory location.
 16. The device according to claim 14, whereinthe first memory location is a flash-type memory and/or the secondmemory location is a SRAM-type memory.
 17. The device according to claim14, wherein the delay of the overlay mechanism is programmable.
 18. Thedevice according to claim 14, wherein the delay of the overlay mechanismis configured to compensate at least partially for a difference betweenaccess times of the first memory location and of the second memorylocation.
 19. The device according to claim 14, wherein the device isconnectable to the first memory location and the second memory locationby at least one bus or by at least one crossbar.
 20. The deviceaccording to claim 19, wherein the device comprises a processor, andwherein the overlay mechanism is configured to delay a processingoperation of the processor requesting access to the first memorylocation or to delay a forwarding of data from the bus or from thecrossbar to the processor, to thereby delay access to the second memorylocation.
 21. The device according to claim 20, wherein the overlaymechanism is configured to delay a processing operation by stalling atleast one cycle of the processor.